Characterization of the uptake of divalent metal ions by a hatchery residual

Hatcheries that supply the U. S. poultry industry with chicks generate large amounts of waste materials that require disposal. A major component of this hatchery residual is eggshell, which is primarily composed of calcium carbonate in the form of calcite. Metal uptake by calcite is known to occur via a complex combination of mechanisms. This work demonstrates that a hatchery residual can also effectively remove several divalent metal cations [Cd(II), Cu(II), Ni(II), Pb(II), and Zn(II)] from dilute aqueous solutions. Mechanisms by which this uptake occurs was evaluated by performing batch equilibrium experiments, column breakthrough and regeneration experiments, and chemical speciation calculations. Dissolution of calcite from the hatchery residual increased solution pH and enhanced metal uptake. Removal selectivity of the hatchery residual decreased according to: Pb(II) > Cu(II) > Zn(II) approximate to Cd(II) > Ni(II), and is attributable, in part, to different removal mechanisms. Chemical speciation calculations suggest that (co) precipitation contributed to the removal of Pb(II) and Cu(II) but was not important for the other metals in the column experiments. Substantial amounts of Cd(II) and Zn(II) could not be recovered using ethylenediamine tetraacetic acid regeneration and may have been incorporated into the calcite lattice, as observed in previous studies. Adsorption also contributed to the removal of all of the metals examined in this study. The hatchery residual may have beneficial uses in metal treatment applications where these properties can be properly exploited.